@phdthesis{Arworn1999,
  author    = {Arworn, Srichan},
  title     = {Groupoids of hypersubstitutions and G-solid varieties},
  address   = {Potsdam},
  pages     = {80 S.},
  year      = {1999},
  language  = {en}
}
@phdthesis{ArwornDenecke1999,
  author    = {Arworn, Srichan and Denecke, Klaus-Dieter},
  title     = {Sets of hypersubstitutions and set-solid varieties},
  year      = {1999},
  language  = {en}
}